Bench Talk

Join journalist Tommy Cummings for a weekly look at all things interesting, new, and noteworthy for design engineers.

It's no fun being tethered, especially when trying to charge a device.

You want the convenience of not having to deal with keeping up with a charging cord for your smartphone or other devices. Now that electric vehicles and wearables are increasing in popularity, you’re dreaming of ways to cut the charging cord, too.

Wireless charging—the method of transmitting energy from a power source to a consuming device without wires or cable—has been around for a while, dating back to inventor Nikola Tesla’s demonstration of wireless power transfer in 1891. More than 130 years later, it's still a growing technology. Designers are coming up with numerous solutions for a wireless charging industry that’s powering forward.

First, let’s review the upsides of wireless charging. Wireless charging is reliable, convenient, and a proven safe technology that eliminates the need for physical connectors and cables. Second, it provides continuous inductive power transfer, provided the charging source and discharged device are closely adjacent and have tightly-coupled compatible coils independent of device type or size—small to industrial.

Wireless charging has its downsides, too. Magnetic fields decay quickly in the air, so wireless charging of current smartphones is limited by distance, and devices are a bit more expensive when you start adding magnetic materials, coils, chips, and related protection circuits.

In this week's New Tech Tuesdays, we'll look at new products from Signal Transformer, PANJIT Semiconductors, and STMicroelectronics which facilitate power-transfer solutions.

We’re probably most familiar with charging pads for smartphones or tablets. These pads employ wireless charging coils that generate an oscillating magnetic field to inductively transfer signals, data, and power from one source to another. The Signal Transformer/Bel Wireless Charging Coils come in single, double, and multiple winding configurations that bridge transmitters and receivers. The low-profile coils are ideal for phones, tablets, gaming controllers, wearable devices, toothbrushes, robotic cleaners, drones, and many smart car charging applications. Inductive coupling, of course, eliminates conductive connections and traditional wiring. In a fixed-in position, the non-moving coils are resistant to vibration and corrosion, which optimizes reliability and longevity.

The PANJIT Power MOSFETs for Wireless Charging Transmitters are optimized to move electromagnetic power from the source to the battery receiver of the application. These power metal-oxide-semiconductor field-effect transistors (MOSFETs) are designed to keep wireless chargers working properly and efficiently. These MOSFETs come in a low-profile package that saves space while delivering low switching losses and high switching frequencies. The MOSFETs have low field-of-merit (FOM), and exposed thermal pads for surface-mount design. Applications include wireless charging pads and cases.

Wireless power solutions also require power receivers. STMicroelectronics' STWLC68 Qi-Compatible Wireless Power Receiver can manage 5W of output power. The STWLC68 rectifies the AC voltage across the receiving coil into a regulated DC voltage at the output. The 32-bit and 64MHz arm Cortex microcontroller supports Qi 1.2.4 specifications for inductive communication protocols and Base Power Profile (BPP), making it ideal for portable devices such as smartphones, power banks, and wearable devices. A low-loss synchronous rectifier and a linear regulator with low drop-out are responsible for the STWLC68's efficiency. The digital core manages them to minimize overall power dissipation over a wide range of output load conditions. Qi (pronounced "chee") is a global wireless charging standard developed by the Wireless Power Consortium.

Wireless charging is a fast-evolving technology with a large potential for market growth. As long as devices are designed to be convenient, so, too, will be the desire to make wirelessly charging them be equally convenient. After all, few people like to be tethered.